Oops: How Long Does it Take You to Catch a Falling Object?

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Author: Janice VanCleave


How long does it take you to catch a falling object?


    table and chair
    yardstick (meterstick)


  1. Sit on the chair with your forearm on the tabletop and your writing hand extending over the edge of the tabletop.
  2. Ask your helper to hold the yardstick (meterstick) so that the bottom of the stick (the zero end) is just above your hand.
  3. Place your thumb and index finger on either side of, but not touching, the bottom of the ruler.
  4. Ask your helper to drop the ruler through your fingers without telling you when it is going to be dropped.
  5. After the ruler is released, try to catch it as quickly as possible between your thumb and fingers.
  6. Observe the number on the ruler just above your thumb. Record this number as the reaction distance.


The distance the stick falls varies with each individual.


The reason that the reaction time will vary with individuals is that when the ruler begins to fall, a message is sent to the brain. Like a computer, the brain takes this input information and, in fractions of a second, sends a message telling the muscles in the hand to contract. The distance the stick falls can be different for each individual because it depends on the time it takes for these impulses to be sorted out by the brain and the output message to be received by the hand's muscles. The sensory nerves in the eye start this relay of messages called nerve impulses. The first stop is in the largest section of the brain called the cerebrum. The cerebrum is where all thoughts occur and where input from sensory nerves is interpreted. The cerebrum sends a message (nerve impulse) to another section of the brain called the cerebellum. The cerebellum brings together all the muscle actions that are necessary to grasp the ruler. This does not have anything to do with how smart you are; instead it compares differences in hand-eye coordination.

Let's Explore

  1. Would practice change the reaction time? Repeat the experiment ten times. Record the reaction time for each trial in a chart similar to the one on page 14 and plot the data on a graph.
  2. Would using a different hand affect the results? Change hands and repeat the experiment. Compare the differences in the improvement of the reaction times for the two hands.
  3. Would distractions affect the results? Have a second helper to ask questions during the experiment. The questions could be simple math problems or anything that requires enough thinking to be distracting. Compare the reaction times with and without distractions.
  4. Does the age of the experimenter affect the reaction time? Ask people of different ages to perform the experiment. Science Fair Hint: Photographs taken during the experiment along with graphs representing the results can be displayed.
  5. Oops



Show Time!

Can the reaction time of animals other than humans be influenced? Find out how dogs, horses, whales, and other animals are trained. A report about training animals can be part of a project. Include in the report answers to such questions as:

  • What stimuli are used to encourage these animals to respond?
  • Which animals respond the fastest?

All living organisms are constantly responding to stimuli around them. Stimuli are things that cause a response in a living organism. A cat hears a bird chirping, and its ears send a message to the brain. The cat may respond to the stimulus (the bird's chirp) in different ways—raising its ears, twitching its tail, or standing alert. Observe and discover other common responses made by animals around you. A diagram, like the one for the cat, can be used to represent the stimulus-response behavior of the animals.

Check it Out!

How do drugs and alcohol affect reaction time? Good sources for information about the affects of drugs would be your teacher, parent, school nurse, and/or physician.

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